Illinois hunters hope to time mallard movement with their midseason hunts. Photos courtesy of Bill Key Early-migrating northern pintails are a common sight along the Illinois and Mississippi rivers. Which birds move early and which wait for winter? By Russ Mason Contributing Writer Some waterfowl are programmed to leave the North well before winter arrives. Others stay as long as open water and available food make survival possible. Understanding the difference helps explain migration patterns – and gives hunters a better idea of when the next flight of birds might arrive. Biologists describe the differences in terms of migratory strategies. Understanding them helps explain why blue-winged teal disappear while mallards remain, or why snow geese move through an area even as some Canada geese settle in for winter. Obligatory and facultative migration Waterfowl migration falls along a continuum rather than into two rigid categories. Obligate migrants follow regular seasonal migration patterns largely governed by biological rhythms. Changes in day length initiate physiological and behavioral preparations for migration. These birds generally travel between northern breeding grounds and southern wintering areas even when northern weather remains relatively mild. Facultative migrants have greater flexibility. They can delay migration when conditions remain favorable, moving when deteriorating weather, frozen wetlands, snow-covered food supplies or other environmental changes make remaining in place less advantageous. Migration is expensive, consuming energy and exposing birds to hazards. When suitable habitat remains available farther north, staying put may offer a survival advantage. Research published in the Journal of Animal Ecology in 2024 confirmed that temperature and precipitation influence fall migration across multiple waterfowl species, although responses vary. Early departures: Teal and northern pintails Blue-winged teal are among North America’s earliest southbound duck migrants. Many begin leaving northern breeding areas in late summer, sometimes before most hunters begin thinking seriously about fall migration. Their departure is driven largely by seasonal biological rhythms rather than freezing temperatures. Bluewings winter primarily in the southern United States, Mexico, Central America and northern South America. Northern pintails are also relatively early migrants. Many begin moving south before winter conditions become severe, using shallow wetlands, flooded agricultural fields and other productive feeding areas along the way. Northern shovelers, gadwalls and wood ducks also frequently make substantial southbound movements before severe winter weather arrives. For hunters, the lesson is straightforward: Early-season opportunities can be excellent for teal and other early migrants. Waiting for the first major cold front may mean missing some of the best local concentrations. Snow geese: Travelers of long distances Snow geese provide a useful contrast to the more weather-dependent behavior of many Canada geese. Their populations follow pronounced annual migrations between Arctic and subarctic breeding grounds and wintering areas farther south. Greater snow geese, for example, breed in the eastern Canadian Arctic and winter primarily along the Atlantic Flyway. Other populations use the Central and Mississippi flyways. These journeys are part of an established seasonal cycle tied to breeding, molting, food availability and winter survival. Snow geese cannot remain indefinitely on northern breeding grounds simply because autumn happens to be mild. Canada geese: Not all geese are alike Northern-breeding Canada geese typically migrate between Canadian breeding grounds and wintering areas in the United States. Other populations breed in temperate regions of the United States and southern Canada and may remain in the same general area year-round. Large Canada geese are remarkably cold-hardy. They can remain in northern areas as long as they can reach waste grain in harvested fields and find open water for resting and roosting. Deep snow can cover food supplies, however, while extensive ice eliminates access to aquatic feeding areas and safe roosting habitat. When those conditions persist, geese often move south. This explains why a flock feeding in a Great Lakes cornfield in November may include northern migrants, local residents or both. Their behavior may look identical, but their subsequent movements can be quite different. Biologists point out that all ducks do not migrate on the same schedule – or for the same reasons. Weather is a major factor but is certainly not only factor, especially in Illinois. Photo courtesy of Bill Key Mallards: Classic migrants dependent on weather Mallards are among North America’s best examples of facultative migration. Their adaptable diet and ability to exploit agricultural foods allow many populations to remain farther north than less flexible species. They feed on seeds, aquatic vegetation, waste grain and other available foods. Where harvested fields provide grain and rivers, springs or other waters remain open, mallards can survive considerable cold. A brief freeze does not necessarily produce a major migration. Birds may wait out cold spells rather than expend the energy required for long-distance travel. The situation changes when persistent snow covers food supplies and ice eliminates access to wetlands. Moving south then becomes a practical necessity. Mallards can also move north again when winter thaws reopen feeding areas. This flexibility helps explain their unpredictable hunting patterns. Diving ducks: Waiting for the big water to freeze Canvasbacks, redheads, scaup, goldeneyes and buffleheads use lakes, bays, reservoirs and other waters. Many depend on aquatic food resources that remain accessible in deeper water after shallow wetlands begin freezing. Consequently, diving ducks can remain north after some dabbling ducks have moved south. Eventually, extensive ice cover forces movement, with timing depending on species, water depth and alternative habitat availability. For hunters, the arrival of diving ducks may depend less on the first hard frost than on conditions across the larger waters where these birds feed. Early November: The first major turning point Species to watch: canvasbacks, scaup, redheads, American wigeon, mallards and Canada geese. Large lakes and bays attract diving ducks, while northern-breeding geese increase in number. Mallards may also arrive following favorable winds. What hunters should look for: large rafts of diving ducks, increasing goose traffic and fresh mallard concentrations. Mid- to late November: Weather’s a bigger player Species to watch: mallards, Canada geese, late-moving diving ducks and remaining northern migrants. Persistent cold, snowfall and ice become increasingly important. Mallards and Canada geese often remain north while food and open water are accessible. What hunters should look for: shrinking open-water areas, abandoned marshes and new concentrations along larger rivers and lakes. A brief cold snap may redistribute birds locally. Prolonged freezing temperatures accompanied by deep snow are more likely to trigger substantial southward movements. December: The freeze-up migration Species to watch: late mallards, Canada geese, common goldeneyes and other late-moving ducks. Widespread ice can produce the final major southbound movements in the Great Lakes region. Some birds remain around open rivers, springs and reservoirs. What hunters should look for: remaining open-water refuges and fields where accessible grain remains available. The three signals worth watching Three field observations are often more informative than the calendar alone: 1. Open water: When shallow wetlands freeze, birds concentrate on deeper lakes and rivers. When those areas freeze, larger movements may follow. 2. Snow cover: Snow hiding waste grain can push mallards and Canada geese out of otherwise-suitable northern habitat. 3. Wind and weather systems: Favorable winds and passing fronts help migrants travel, while sustained cold and snow change where birds can feed and rest. Hunters should also distinguish migration from redistribution. Birds shifting among nearby lakes, marshes and agricultural fields have not necessarily begun a long-distance journey. The takeaway Some waterfowl move because the season tells them it is time to go. Others move when conditions make staying too costly. Early migrants, such as blue-winged teal, offer opportunities before severe weather arrives. Snow geese follow pronounced seasonal routes. Northern Canada geese and mallards wait until snow and ice restrict food and open water. Diving ducks can remain as long as their preferred waters remain productive. For waterfowl hunters, understanding these differences provides a better framework for predicting migration than watching the thermometer alone. The calendar tells you which birds may be coming; habitat and weather help explain when they are likely to move.